Technique to simultaneously distribute clock signals and data on integrated circuits, interposers, and circuit boards

ABSTRACT

A technique is described for simultaneously and synchronously transmitting digital data and a clock signal in a digital integrated circuit, circuit board, or system. The technique is based on the phase shift keying (PSK) modulation of an RF high frequency carrier which is distributed on low impedance interconnection transmission lines. The PSK modulation contains the digital data while the carrier itself constitutes the clock signal, and the clock signal and digital data are transmitted in a synchronous manner. The carrier frequency may be near f T , the maximum operation frequency of the transistors. Since the digital data and clock signal are simulaneously transmitted on the same interconnection, the digital data never becomes skewed with respect to the clock signal, or vice versa.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the timing of clock and data signals in integrated circuits. More specifically, the invention relates to simultaneous transmission of digital data and clock signals to eliminate skewing of the data and clock signals with respect to each other.

2. State of the Art

Digital integrated circuits typically include multiple logic elements, with the timing of operation of each logic element controlled by a clock signal. It is common for an integrated circuit chip to have one central clock generator, with the signal from the clock generator being distributed around the integrated circuit via clock-line interconnects. An important consideration in the design of digital integrated circuits is the timing of the arrival of clock and data signals at various logic elements.

Variation in clock signal arrival time is referred to as clock skew. A variety of techniques have been used to provide clock connections that are symmetrical and all of the same length in order to minimize clock skew at the various logic elements, including, for example, the methods of Yip and Carrig. See, K. Yip, “Clock tree distribution: balance is essential for a deep-submicron ASIC design to flourish,” IEEE Potentials, vol. 16, no. 2, pp. 11-14, April-May 1997; and K. M. Carrig et al., “Clock methodology for high-performance microprocessors,” Proc. Custom Integrated Circuits Conference, Santa Clara, Calif., May 5-8, pp. 119-122, 1997. A number of prior art approaches are illustrated in FIGS. 1A-1D.

FIG. 1A illustrates an H-tree clock-distribution, which is used primarily in custom layouts and has varying tree interconnect segment widths to balance skew throughout the chip.

FIG. 1B shows a clock grid clock-distribution structure. The clock grid is the simplest clock-distribution structure and has the advantage of being easy to design for low skew. However, it is area inefficient and power hungry because of the large amount of clock interconnect required. Nevertheless, some chip vendors are using this clock structure for microprocessors.

FIG. 1C depicts a balanced tree clock-distribution structure. The balanced tree is the clock-distribution structure most commonly used in high performance chips. See, J. L. Neves et al., “Automated synthesis of skew-based clock-distribution networks,” VLSI Design, vol. 7, no. 1, pp. 31-57, 1998. In order to carry current to the branching segments, the clock line is widest at the root of the tree and becomes progressively narrower at each branch. As a result, the clock line capacitance increases exponentially with distance from the leaf cell (clocked element) in the direction of the root of the tree (clock input). Moreover, additional chip area is required to accommodate the extra clock line width in the regions closer to the root of the tree.

As shown in FIG. 1D, buffers may be added at the branching points of the balanced tree structure. Adding buffers at the branching points of the tree significantly lowers clock interconnect capacitance, because it reduces the clock line width required toward the root.

One prior art alternative to generating clock signals centrally and distributing them about the chip is to partition the chip design into blocks, as shown in FIG. 2. A synchronous clock signal is used only within a single block, while communication between different blocks is performed on an asynchronous basis. See, T. Meincke et al., “Globally asynchronous locally synchronous architecture for large high-performance ASICs,” IEEE Symposium On Circuits and Systems, Orlando, Fla., 30 May-2 June, Vol. 2, pp. 512-515, 1999.

In the past, clock design has not typically been considered within the context of full chip timing. Existing design methodologies typically treat clock skew as a problem to be eliminated, and most designers strive to achieve zero skew. However, producing clock signals with zero skew may not be the optimum way to achieve either the safest or the highest performance clock design. It is often the case that, even after zero skew is attained, chip failures are caused by simultaneous switching current or other timing related problems.

There remains a need for a method of coordinating the timing of clock and data signals on a chip that can be achieved with a simple design and minimum number of critical paths on the chip. It would be desirable to reduce the power consumption associated with clock-distribution lines or other chip timing circuitry. It would also be desirable to reduce the sensitivity of chip timing to process variations and various intermittent noises. Finally, there is an ongoing need for the development of higher speed methods for clocking data to provide enhanced chip performance.

BRIEF SUMMARY OF THE INVENTION

The methodology of the present invention addresses the problem of meeting a chip's timing requirements by combining clock timing with data path timing. Clock skew is treated not as a problem but as a controllable design variable which may be used to optimize overall chip timing. The invention achieves simultaneous distribution of clock and data signals by performing phase shift keying of digital data signals on clock frequency AC carrier signals, transmitting the keyed signals to different locations on the chip, and demodulating the keyed signals to retrieve digital data and clock signals. The inventive method may be used for signal interconnections on integrated circuits, interposers, and circuit boards.

The present invention reduces the number of critical paths on the chip in order to simplify designs and achieve timing closure. The present invention also allows increased clock frequency, thereby improving chip performance. Further, the present invention increases tolerance of chip timing to process variations and intermittent noise. The present invention may be used to create a larger timing budget to reduce power consumption. The present invention may also be used to reduce peak current and simultaneous switching noise to eliminate interference between digital and analog circuits.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:

FIG. 1A shows a prior art H-tree clock-distribution structure;

FIG. 1B shows a prior art clock grid clock-distribution structure;

FIG. 1C shows a prior art balanced tree clock-distribution structure;

FIG. 1D shows a prior art balanced tree clock-distribution structure that includes buffers at branching points for reduction of clock-interconnect capacitance;

FIG. 2 illustrates a prior art method of partitioning a system into multiple blocks;

FIG. 3 is a block diagram of a device including circuitry for phase shift keying and demodulation of clock and digital data signals according to the present invention;

FIG. 4 is a block diagram depicting components of the inventive system used to perform differential Phase Shift Keying of digital data and clock signals;

FIG. 5 depicts a lead phase shift network used in the block diagram of FIG. 4;

FIG. 6 depicts a lag phase shift network used in the block diagram of FIG. 4;

FIG. 7A illustrates the signal V_(x)=A sin(ωt+φ) output by the lead phase shift network of FIG. 5;

FIG. 7B shows the signal V_({overscore (x)})=A sin(ωt−φ) output by the lag phase shift network of FIG. 6;

FIG. 8 shows a demodulator circuit for recovering digital data from differential Phase Shift Keyed signals; and

FIG. 9 shows circuitry for recovering a clock signal from differential Phase Shift Keyed signals.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, analog signal techniques are used for signal interconnections on integrated circuits, interposers, and circuit boards. The clock signal is used as a high frequency carrier for signal interconnection and is modulated by the digital data using phase shift keying (PSK). PSK refers to a modulation technique that alters the phase of the carrier. Binary phase shift keying (BPSK), which is used in the present invention, has two phases, represented by the binary values 0 and 1. PSK is a special type of amplitude modulation, or a type of amplitude shift keying (ASK) which creates signals having values −1 or 1, and its bandwidth is the same as that of ASK. The inventive method includes the use of binary phase shift keying and low frequency differential modulation of the phase of a high frequency carrier. This approach results in a narrow bandwidth of the modulated signal comparable to that obtained with simple amplitude shift keying.

FIG. 3 is a block diagram of a device 2 including circuitry for performing phase shift keying of clock and digital data signals and subsequent demodulation of the PSK signals to retrieve the clock and digital data signals. Device 2 may be an integrated circuit, interposer, circuit board, or similar device. Device 2 includes phase shift keying circuitry 4, which performs phase shift keying of the digital data signal X onto the clock signal CLK to generated phase shift keyed signals V_(x) and V_({overscore (x)}). Phase shift keying circuitry 4 is located near the clock source on device 2. PSK signals V_(x) and V_({overscore (x)}) are transmitted on interconnection lines 9 and 13 to digital signal demodulator 6. Digital signal demodulator 6 demodulates PSK signals V_(x) and V_({overscore (x)}) to retrieve digital data signal X. Digital data signal X and PSK signals V_(x) and V_({overscore (x)}) are input to clock signal demodulator 8, which demodulates PSK signals V_(x) and V_({overscore (x)}) to retrieve the clock signal. The clock signal and digital data signal X are input to clocked element 10 with no relative time delay between the two. Digital signal demodulator 6 and clock signal demodulator 8 are located close to clocked element 10 but may be located at some distance from phase shift keying circuitry 4.

FIG. 4 is a schematic diagram of differential phase shift keying circuitry 4 that may be used to perform the differential phase shift keying signal interconnection technique of the present invention. A sinusoidal oscillator signal sin(ωt) having a radian frequency ω at the clock signal frequency for the chip is generated by oscillator 1. The oscillator signal is sent simultaneously to phase shifter 3 and phase shifter 5. Digital signal X is input to phase shifter 3 and controls the phase shift produced in the oscillator signal by phase shifter 3, while the complementary digital signal {overscore (X)} is input to and controls the phase shift produced in the oscillator signal by phase shifter 5. The output of phase shifter 3 is fed to driver amplifier 7 and, from there, transmitted on interconnection line 9. The output of phase shifter 5 is fed to driver amplifier 11 and subsequently transmitted on interconnection line 13. Interconnection line 9 and interconnection line 13 are low impedance interconnection lines with matched terminating impedances 15 and 17, respectively.

As shown in FIG. 5, phase shifter 3 is a lead phase shift network made up of capacitor 19 and voltage variable resistor 21 forming a high pass filter. Capacitor 19 has a capacitance C1 and voltage variable resistor 21 has a resistance of R1. Voltage variable resistor 21 is an NMOS transistor configured as a voltage variable resistor, with digital signal X connected to its gate to regulate the value of resistance R1. Phase shifter 3 produces a positive phase shift φ in the input signal when X has a logical high value. Thus, when the input to phase shifter 3 is sin(ωt) and X has a logical high value, the output will be V_(x)=A sin(ωt+φ), and when X has a logical low value, the output will be V_(x)=A sin(ωt), where A is an arbitrary constant. V_(x) is plotted in FIG. 7A.

FIG. 6 depicts phase shifter 5, which is a lag phase shift network made up of voltage variable resistor 23 and capacitor 25 forming a low pass filter. Capacitor 25 has a capacitance C2 and voltage variable resistor 23 has a resistance of R2. Voltage variable resistor 23 is an NMOS transistor configured as a voltage variable resistor, with complementary digital input {overscore (X)} connected to its gate to regulate the value of resistance R2. Phase shifter 5 produces a phase shift of equal magnitude but opposite sign to that produced by phase shifter 3; thus, it produces a negative phase shift φ in the input signal. Thus, when the input to phase shifter 5 is sin(ωt) and {overscore (X)} has a logical high value, the output will be V_({overscore (x)})=A sin(ωt−φ), and when {overscore (X)} has a logical low value, the output will be V_({overscore (x)})=A sin(ωt) where A is the arbitrary constant found in the expression for V_(x). V_({overscore (x)}) is plotted in FIG. 7B.

Both phase shifter 3 and phase shifter 5 utilize phase shift networks of the type used in high frequency ring oscillators as disclosed in U.S. patent application Ser. No. 09/860,131, filed May 17, 2001, in which the frequency of oscillation can be near f_(T) of the transistors.

The phase shift keyed signals V_(x) and V_({overscore (x)}) are transmitted on matched interconnection lines 9 and 13 to the vicinity of the clocked element 10. V_(x) and V_({overscore (x)}) each contain both clock and phase shift keyed digital data. Any signal skew which occurs over the length of interconnection lines 9 and 13 should be substantially the same for the signals on the two interconnection lines. At the clocked element 10, PSK signals V_(x) and V_({overscore (x)}) are demodulated to recover the digital signal X and the clock signal.

Digital signal demodulator 6, which is used to demodulate the digital signal encoded in signals V_(x) and V_({overscore (x)}), is depicted in FIG. 8. Digital signal demodulator 6 includes differential amplifier 27, transistor amplifier circuit 29 which functions as an inverter or single stage amplifier, RC filter 31, and comparator 33. Signals V_(x) and V_({overscore (x)}) are fed into the positive and negative inputs, respectively, of a differential amplifier 27. The difference between V_(x) and V_({overscore (x)}) is V_(x)−V_({overscore (x)})=A sin(ωt+φ)−A sin((ωt−φ)=2A cos(ωt)sin(φ) when X has a logical high value. When X has a logical low value, V_(x)−V_({overscore (x)})=0. As noted previously, A is an arbitrary constant amplitude, ω is the radian frequency of the carrier or oscillator frequency and φ is the amount of phase modulation at the input. Since φ, the amount of phase modulation, only has two values, zero and some finite value, then the differential output of the receiver is a pulse modulated sine or cosine wave at the carrier frequency.

Transistor amplifier circuit 29 is made up of diode-connected PMOS load transistor 35 and NMOS transistor 37. The demodulator circuit of FIG. 8 takes advantage of the nonlinear characteristics of PMOS load transistor 35 to recover digital data from PSK signals. For simplicity, it can be assumed that PMOS load transistor 35 and NMOS transistor 37 have matching characteristics. Power supply voltage V_(DD) is connected to the source of PMOS load transistor 35. Power supply voltage V_(DD)=4V_(T), where V_(T) is the threshold voltage of the PMOS load transistor 35 and NMOS transistor 37. The nominal DC voltage at the output of differential amplifier 27 and the input of transistor amplifier circuit 29 is 2V_(T) when no AC signal is output by differential amplifier 27. The corresponding voltage at the output of transistor amplifier circuit 29 is also 2V_(T). When V_(x) and V_({overscore (x)}) are applied to the inputs of differential amplifier 27, the output is: V₁=2V_(T)+2Acos(ωt)sin(φ) when X has a logical high value and V₁=2V_(T) when X has a logical low value.

If the signal amplitude 2A is made comparable to V_(T) of the transistors, the output from transistor amplifier circuit 29 is: V ₂=2V_(T)−2A cos(ωt)sin(φ)−[4A²/(4V_(T))]cos ²(ωt)sin ²(φ), which, as can be seen, includes a component that depends on the square of the AC component of the input signal.

RC filter 31, which is a simple RC low pass filter at the output of transistor amplifier circuit 29, is made up of resistor 39 having a resistance R3 and capacitor 41 having a capacitance C3. The output of RC filter 31 is: V ₃=2V_(T)−½[(4A²/(4V_(T)))sin ²(φ)], which is the DC component of the output of transistor amplifier circuit 29 and corresponds to the average value of cosine squared. Signal V₃ is input to comparator 33 and compared to reference signal V_(ref)=2V_(T) to produce an output signal V₄ which has a value of either sin ²(φ) or zero. V₄ is the recovered digital data signal.

FIG. 9 illustrates the circuitry of clock signal demodulator 8, which is used to recover the clock signal from the modulated RF carrier. Also shown are matched output impedances 15 and 17 of interconnection lines 9 and 13, respectively.

Clock signal demodulator 8 includes two phase shift networks, lag phase shift network 43 and lead phase shift network 45. Lag phase shift network 43 includes a low pass filter made up of voltage variable resistor 47 having resistance R4 and capacitor 49 having resistance C4. The input to lag phase shift network 43 is signal V_(x) from interconnection line 9. Voltage variable resistor 47 is an NMOS transistor configured as a voltage variable resistor. The resistance R4 of voltage variable resistor 47 is controlled by voltage V₅, which is connected to the gate of the NMOS transistor. V₅=V_(DC)−BV₄, where V_(DC) is a constant DC voltage, B is an arbitrary constant, and V₄ is the recovered digital signal output by the demodulator circuit shown in FIG. 8. The output of lag phase shift network 43 is fed into driver amplifier 51. The output of driver amplifier 51 is V₇=D sin(ωt+φ−θ), where D is an arbitrary constant, ω is the radian frequency of the clock signal, φ is the phase shift introduced by phase shifter 3 during phase shift keying of the digital data, and θ is the phase shift introduced by lag phase shift network 43.

Lead phase shift network 45 includes a high pass filter made up of capacitor 53 having capacitance C5 and voltage variable resistor 55 having resistance R5. The input to lead phase shift network 45 is signal V_({overscore (x)}) from interconnection line 13. Voltage variable resistor 55 is an NMOS transistor configured as a voltage variable resistor. The resistance R5 of voltage variable resistor 55 is controlled by voltage V₆, which is connected to the gate of the NMOS transistor. V₆=V_(DC)+BV₄, where V_(DC), B, and V₄ are as defined previously. The output of lead phase shift network 45 is fed into driver amplifier 57. The output of driver amplifier 57 is V₈=D sin(ωt−φ+θ), where D is the same arbitrary constant as found in the equation for V₇, ω is the radian frequency of the clock signal, φ is the phase shift introduced by phase shifter 5 during phase shift keying of the digital data, and θ is the phase shift introduced by lead phase shift network 45.

In lag phase shift network 43 and lead phase shift network 45, changing the resistance values R4 and R5 changes the phase shift of each network. In lead phase shift network 45, decreasing R5 increases the phase shift θ, making it more positive, since the corner frequency, ω_(c), moves up closer to the carrier frequency, ω. In lag phase shift network 43, increasing R4 lowers the comer frequency ω_(c) and makes θ more negative, or shifts the phase of the incoming signal to more negative values.

The gains and characteristics of lag phase shift network 43 and lead phase shift network 45 are adjusted so that φ=θ. An analog adder 59 made up of resistors 61, 63, and 65 and amplifier 67 is used to average signals V₇ and V₈ to reduce noise and errors and yield output V₉, which equals the clock signal sin(ωt) without the modulation of the digital data. In this manner, the clock signal can be recovered.

The frequency limiting element in this system is not the oscillator, carrier frequency, digital modulation frequency, or line characteristics but, rather, is likely to be the receiver amplifier. By using a relatively small number of CMOS elements in the circuitry of the invention, power consumption is kept low. The novel PSK method allows clock and data signals to be transmitted over any distance and to remain synchronized with each other. Speed and performance of the device is thus enhanced. 

1. A device for delivering a clock signal and a digital signal in synchronization to a clocked element of a semiconductor device, comprising: a phase shift keying circuit for performing phase shift keying of said digital signal onto said clock signal to create a lead output signal and a lag output signal; a digital signal demodulator for demodulating said lead output signal and said lag output signal from said phase shift keying circuit to retrieve said digital signal; and a clock signal demodulator for demodulating said lead output signal and said lag output signal in conjunction with said digital signal to retrieve said clock signal.
 2. The device of claim 1, wherein said phase shift keying circuit comprises: an oscillator for producing a sinusoidal oscillator signal; a lead phase shift network for receiving said sinusoidal oscillator signal and said digital signal and producing a positive phase shift in said lead output signal when said digital signal has a logical high value; and a lag phase shift network for receiving said sinusoidal oscillator signal and a complementary digital signal and producing a negative phase shift in said lag output signal when said complementary digital signal has a logical high value.
 3. The device of claim 2, wherein said lead phase shift network comprises a capacitor and a voltage variable resistor forming, in combination, a high pass filter.
 4. The device of claim 2, wherein said lead phase shift network comprises: a capacitor having a first terminal for receiving said sinusoidal oscillator signal and a second terminal; a driver amplifier connected to said second terminal of said capacitor for driving said lead output signal; and an NMOS transistor configured as a voltage variable resistor having a drain connected to said digital signal for controlling a resistance of said NMOS transistor, said NMOS transistor being connected between said capacitor and said driver amplifier.
 5. The device of claim 2, wherein said lag phase shift network comprises a voltage variable resistor and a capacitor forming, in combination, a low pass filter.
 6. The device of claim 2, wherein said lag phase shift network comprises: an NMOS transistor configured as a voltage variable resistor having a drain connected to said complementary digital signal for controlling a resistance of said NMOS transistor and for receiving said sinusoidal oscillator signal; a driver amplifier connected to said NMOS transistor for driving said lag output signal; and a capacitor connected between said NMOS transistor and said driver amplifier.
 7. The device of claim 2, wherein said lead output signal comprises a voltage represented by the function V _(x) =A sin(ωt+φ) when said digital signal has a logical high value and a voltage represented by the function V_(x)=A sin (ωt) when said digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 8. The device of claim 2, wherein said lag output signal comprises a voltage represented by the function V_({overscore (x)})=A sin(ωt−φ) when said complementary digital signal has a logical high value and a voltage represented by the function V_({overscore (x)})=A sin (ωt) when said complementary digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 9. The device of claim 2, wherein said phase shift in said lead output signal and said lag output signal are of equal magnitude but having opposite signs.
 10. The device of claim 1, wherein said digital signal demodulator comprises: a differential amplifier for comparing said lead output signal and said lag output signal to produce a differential output signal; a transistor amplifier circuit for receiving said differential output signal and producing a transistor signal dependent upon the square of an AC component of said differential output signal; an RC low pass filter for receiving said transistor signal and outputting a voltage signal; and a voltage comparing circuit for receiving said voltage signal and a voltage reference signal to produce said digital signal.
 11. The device of claim 10, wherein said differential amplifier comprises a differential amplifier for producing a differential output signal having a voltage represented by the function V=2 V _(T) +2 A cos(ωt)sin(φ) when said lead output signal and said lag output signal are phase shifted, wherein V_(T) is a threshold voltage of a set of transistors in said transistor amplifier circuit, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 12. The device of claim 10, wherein said transistor amplifier circuit comprises: a PMOS load transistor having a PMOS source, a PMOS gate connected to said PMOS source, and a PMOS drain connected to a power supply voltage; and an NMOS transistor having a gate connected to said differential output signal, a source connected to ground, and a drain connected to said PMOS source and said PMOS gate, wherein said PMOS load transistor and said NMOS transistor produce said transistor signal dependent upon the square of an AC component of said differential output signal.
 13. The device of claim 12, wherein said power supply voltage is four times a threshold voltage of said PMOS load transistor and said NMOS transistor.
 14. The device of claim 12, wherein said transistor amplifier circuit comprises a transistor amplifier circuit for producing said transistor signal having a voltage represented by the function V=2V _(T) −2 A cos(ωt)sin(φ)−[4A²/(4V _(T) )]cos ²(ωt)sin²(φ) when said lead output signal and said lag output signal are phase shifted, wherein V_(T) is a threshold voltage of said PMOS load transistor and said NMOS transistor, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 15. The device of claim 10, wherein said RC low pass filter comprises a resistor and a capacitor configured, in combination, to convert said transistor signal to said voltage signal having a voltage V=2 V _(T) −½[(4A²/(4V_(T)))sin²(φ)], wherein V_(T) is a threshold voltage of a set of transistors in said transistor amplifier circuit, A is an arbitrary constant, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 16. The device of claim 1, wherein said clock signal demodulator comprises: a lag phase shift network for receiving said lead output signal and removing a positive phase shift of said lead output signal to recover a first clock signal; a lead phase shift network for receiving said lag output signal and adding a negative phase shift of said lag output signal to recover a second clock signal; and an analog adder for receiving said first clock signal and said second clock signal and averaging said first clock signal and said second clock signal and reducing noise thereon to produce said clock signal.
 17. The device of claim 16, wherein said lag phase shift network comprises a low pass filter including a voltage variable resistor and a capacitor.
 18. The device of claim 16, wherein said lag phase shift network further comprises: an NMOS transistor configured as a voltage variable resistor having a drain connected to a first voltage source for controlling a resistance of said NMOS transistor and for receiving said lead output signal; a driver amplifier connected to said NMOS transistor for driving said first clock signal; and a capacitor connected between said NMOS transistor and said driver amplifier.
 19. The device of claim 18, wherein said first voltage source comprises a voltage V represented by the equation: V=V _(DC) −BV _(D) where V_(DC) is a constant DC voltage, B is an arbitrary constant, and V_(D) is said digital signal from said digital signal demodulator.
 20. The device of claim 16, wherein said lead phase shift network comprises a high pass filter including a capacitor and a voltage variable resistor.
 21. The device of claim 16, wherein said lead phase shift network further comprises: a capacitor having a first terminal for receiving said lag output signal and a second terminal; a driver amplifier connected to said second terminal of said capacitor for driving said second clock signal; and an NMOS transistor configured as a voltage variable resistor having a drain connected to a second voltage source for controlling a resistance of said NMOS transistor, said NMOS transistor connected between said capacitor and said driver amplifier.
 22. The device of claim 21, wherein said second voltage source comprises a voltage V represented by the equation: V=V _(DC) +BV _(D) where V_(DC) is a constant DC voltage, B is an arbitrary constant, and V_(D) is said digital signal from said digital signal demodulator.
 23. The device of claim 16, wherein said analog adder comprises: a set of resistors for reducing noise on said first clock signal and said second clock signal; and an amplifier in combination with a resistor for receiving said first clock signal and said second clock signal to average and produce said clock signal.
 24. A device for performing phase shift keying of a digital signal, comprising: an oscillator for producing a sinusoidal oscillator signal; a lead phase shift network receiving said sinusoidal oscillator signal and said digital signal for producing a positive phase shift in a lead output signal when said digital signal has a logical high value; and a lag phase shift network receiving said sinusoidal oscillator signal and a complementary digital signal for producing a negative phase shift in a lag output signal when said complementary digital signal has a logical high value.
 25. The device of claim 24, wherein said lead phase shift network comprises a capacitor and a voltage variable resistor forming, in combination, a high pass filter.
 26. The device of claim 24, wherein said lead phase shift network comprises: a capacitor having a first terminal for receiving said sinusoidal oscillator signal and a second terminal; a driver amplifier connected to said second terminal of said capacitor for driving said lead output signal of said lead phase shift network; and an NMOS transistor configured as a voltage variable resistor having a drain connected to said digital signal for controlling a resistance of said NMOS transistor, said NMOS transistor connected between said capacitor and said driver amplifier.
 27. The device of claim 24, wherein said lag phase shift network comprises a voltage variable resistor and a capacitor forming, in combination, a low pass filter.
 28. The device of claim 24, wherein said lag phase shift network comprises: an NMOS transistor configured as a voltage variable resistor having a drain connected to said complementary digital signal for controlling a resistance of said NMOS transistor and for receiving said sinusoidal oscillator signal; a driver amplifier connected to said NMOS transistor for driving said lag output signal of said lag phase shift network; and a capacitor connected between said NMOS transistor and said driver amplifier.
 29. The device of claim 24, wherein said lead output signal from said lead phase shift network comprises a voltage represented by the function V _(x) =A sin(ωt+φ) when said digital signal has a logical high value and a voltage represented by the function V_(x)=A sin (ωt) when said digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 30. The device of claim 24, wherein said lag output signal from said lag phase shift network comprises a voltage represented by the function V_({overscore (x)})=A sin(ωt−φ) when said complementary digital signal has a logical high value and a voltage represented by the function V_({overscore (x)})=A sin (ωt) when said complementary digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 31. The device of claim 24, wherein said phase shift in said lead output signal and said lag output signal are of equal magnitude but having opposite signs.
 32. A device for demodulating a phase shift keyed signal from a lead signal and a lag signal, comprising: a differential amplifier for comparing said lead signal and said lag signal to produce a differential output signal; a transistor amplifier circuit for receiving said differential output signal and producing a transistor signal dependent upon the square of an AC component of said differential output signal; an RC low pass filter for receiving said transistor signal and outputting a voltage signal; a voltage comparing circuit for receiving said voltage signal and a voltage reference signal to produce a demodulated digital data signal.
 33. The device of claim 32, wherein said differential amplifier comprises a differential amplifier for producing a differential output signal having a voltage represented by the function V=2 V _(T) +2 A cos(ωt)sin(φ) when said lead signal and said lag signal are phase shifted, wherein V_(T) is a threshold voltage of a set of transistors in said transistor amplifier circuit, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead signal and said lag signal.
 34. The device of claim 32, wherein said transistor amplifier circuit comprises: a PMOS load transistor having a PMOS source, a PMOS gate connected to said PMOS source, and a PMOS drain connected to a power supply voltage; and an NMOS transistor having a gate connected to said differential output signal, a source connected to ground, and a drain connected to said PMOS source and said PMOS gate, wherein said PMOS load transistor and said NMOS transistor produce said transistor signal dependent upon the square of an AC component of said differential output signal.
 35. The device of claim 34, wherein said power supply voltage is four times a threshold voltage of said PMOS load transistor and said NMOS transistor.
 36. The device of claim 34, wherein said transistor amplifier circuit comprises a transistor amplifier circuit for producing said transistor signal having a voltage represented by the function V=2V _(T) −2 A cos(ωt)sin(φ)−[4A²/(4V_(T))]cos²(ωt)sin²(φ) when said lead signal and said lag signal are phase shifted, wherein V_(T) is a threshold voltage of said PMOS load transistor and said NMOS transistor, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead signal and said lag signal.
 37. The device of claim 32, wherein said RC low pass filter comprises a resistor and a capacitor configured, in combination, to convert said transistor signal to said voltage signal having a voltage V=2 V _(T) −½[(4A²/(4V_(T)))sin²(φ)], wherein V_(T) is a threshold voltage of a set of transistors in said transistor amplifier circuit, A is an arbitrary constant, and φ is the amount of phase shift in said lead signal and said lag signal.
 38. A method of synchronizing clock signals and digital data signals on an integrated circuit chip, comprising: generating a sinusoidal oscillator signal, a digital signal and a complementary digital signal; creating a lead output signal from said sinusoidal oscillator signal and said digital signal; creating a lag output signal from said sinusoidal oscillator signal and said complementary digital signal; transmitting said lead output signal and said lag output signal on matched interconnection lines to a vicinity of a clocked element; demodulating said lead output signal and said lag output signal for retrieving said digital signal; demodulating said lead output signal and said lag output signal using said digital signal for retrieving a clock signal; and inputting said digital signal and said clock signal into said clocked element.
 39. The method of claim 38, wherein said creating a lead output signal comprises creating a lead output signal having a positive phase shift when said digital signal has a logical high value.
 40. The method of claim 38, wherein said creating a lead output signal comprises creating a voltage signal V_(x) represented by the function V _(x) =A sin(ωt+φ) when said digital signal has a logical high value and creating a voltage signal V_(x) represented by the function V_(x)=A sin(ωt) when said digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 41. The method of claim 38, wherein creating said lag output signal comprises creating a lag output signal having a negative phase shift when said complementary digital signal has a logical high value.
 42. The method of claim 38, wherein creating said lag output signal comprises creating a voltage signal V_({overscore (x)}) represented by the function V_({overscore (x)})=A sin(ωt−φ) when said complementary digital signal has a logical high value and creating a voltage signal V_({overscore (x)}) represented by the function V_({overscore (x)})=A sin(ωt) when said complementary digital signal has a logical low value, wherein A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift.
 43. The method of claim 38, wherein creating said lead output signal and said lag output signal comprises: creating a lead output signal having a positive phase shift φ; and creating a lag output signal having a negative phase shift φ, wherein said positive phase shift φ and said negative phase shift φ are of equal magnitude.
 44. The method of claim 38, wherein demodulating said lead output signal and said lag output signal for retrieving said digital signal comprises: comparing said lead output signal and said lag output signal for producing a differential output signal; producing a signal dependent upon the square of an AC component of said differential output signal for creating a voltage signal; and comparing said voltage signal and a voltage reference signal for producing said digital signal.
 45. The method of claim 44, further comprising producing a differential output signal having a voltage represented by the function V=2 V _(T) +2 A cos(ωt)sin(φ) when said lead output signal and said lag output signal are phase shifted, wherein V_(T) is a threshold voltage, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 46. The method of claim 44, wherein said producing a signal dependent upon the square of an AC component of said differential output signal comprises producing a signal having a voltage represented by the function V=2V _(T) −2 A cos(ωt)sin(φ)−[4A²/(4V_(T))]cos ²(ωt)sin ²(φ) when said lead output signal and said lag output signal are phase shifted, wherein V_(T) is a threshold voltage, A is an arbitrary constant, ω is the oscillator frequency, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 47. The method of claim 44, further comprising creating a voltage signal having a voltage V=2 V _(T) −½[(4A²/(4V_(T)))sin²(φ)] from said signal, wherein V_(T) is a threshold voltage, A is an arbitrary constant, and φ is the amount of phase shift in said lead output signal and said lag output signal.
 48. The method of claim 38, wherein demodulating said lead output signal and said lag output signal knowing said digital signal for retrieving said clock signal comprises: removing a positive phase shift from said lead output signal for producing a first clock signal; removing a negative phase shift from said lag output signal for producing a second clock signal; and averaging said first clock signal and said second clock signal for retrieving said clock signal. 